Public domain data

These data have no specific confidentiality restrictions for users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.

The recommended acknowledgment is

"This study uses data from the data source/organisation/programme, provided by the British Oceanographic Data Centre and funded by the funding body."

Neil Brown MK3 CTD

The Neil Brown MK3 conductivity-temperature-depth (CTD) profiler consists of an integral unit containing pressure, temperature and conductivity sensors with an optional dissolved oxygen sensor in a pressure-hardened casing. The most widely used variant in the 1980s and 1990s was the MK3B. An upgrade to this, the MK3C, was developed to meet the requirements of the WOCE project.

The MK3C includes a low hysteresis, titanium strain gauge pressure transducer. The transducer temperature is measured separately, allowing correction for the effects of temperature on pressure measurements. The MK3C conductivity cell features a free flow, internal field design that eliminates ducted pumping and is not affected by external metallic objects such as guard cages and external sensors.

Additional optional sensors include pH and a pressure-temperature fluorometer. The instrument is no longer in production, but is supported (repair and calibration) by General Oceanics.

RRS Charles Darwin 62 CTD Data Documentation

Introduction

Instrumentation and Methodology

Instrumentation Summary

The CTD profiles were taken with a Neil Brown Systems MkIIIb CTD mounted beneath a bottle rosette. The CTD was fitted with a pressure sensor, conductivity cell, platinum resistance thermometer, a dissolved oxygen sensor, a Sea Tech 100cm path transmissometer and an IOS 10kHz pinger.

Data Acquisition

Lowering rates for the CTD package were generally in the range 0.5-1.0ms -1 but could be up to 1.5ms -1 . CTD data were logged at 16 frames per second. The CTD deck unit passes raw data to a dedicated Level A microcomputer where 1 second averages are assembled. During this process the Level A calculates the rate of change of temperature and a median sorting routine detects and removes pressure spikes. These data are sent to the Level B for archival. The data are then passed to a Level C workstation for conversion to Pstar format and calibration.

A total of 96 stations (01 - 96) were occupied, of which 93 used the MkIIIb CTD. A Neil Brown MkV CTD was used at 3 of the stations. Data for stations 79-81 are from full depth casts using this instrument. Two trials had previously been conducted at stations 72 and 76.

Data Processing

The 1 second data passed to the Level C were converted to Pstar format and initially calibrated with coefficients from laboratory calibrations. The up cast data were extracted for merging with the bottle firing codes, on time, thus the CTD variables were reconciled with the bottle samples. Final calibrations were applied using the sample bottle data. The data were worked up to WOCE standards by the data originators before being supplied to BODC.

BODC Data Processing

No further calibrations were applied to the data received by BODC. BODC were mainly concerned with the screening and banking of the data.

The data were converted into the BODC internal format (PXF) to allow the use of in-house software tools, notably the graphics editor. Oxygen was converted to umol/l.

Spikes in the data were manually flagged 'suspect' by modification of the associated quality control flag. In this way none of the original data values were edited or deleted during quality control. These data from cruise CD62 required little flagging and just a few points were set suspect. Profiles 079, 080, and 081 were made using the MkV CTD and have null attenuance.

Once screened, the CTD data were loaded into a database under the Oracle relational database management system. The start time stored in the database is the CTD deployment time, and the end time is the time the CTD was removed from the water. Actually these times are more precisely the start and end of data logging. Latitude and longitude are the mean positions between the start and end times calculated from the master navigation in the binary merged file. The longitude given to the end time for station 62 in the cruise report is incorrect and should be closer to -35 50.0.

Potential attenuance was converted to attenuance from within Oracle as follows:

atten = exp (-atten)

atten = atten / (1.0 -ln (atten) x press / 215800)

atten = -ln (atten)

The following comparison was made between the maximum CTD pressure and bottle firing pressure:

STATION

MAX (CTD)

MAX (BOT)

62019

969

973

62021

2043

2049

62042

2973

3202

62086

557

506

62088

967

755

For stations 62019, 62021 and 62042 the tail end of the CTD cast might have been edited out by the originating scientists. For station 62086 there were null entries for CTDPRS, CTDTMP and CTDSAL for bottle 1 (REVPRS = 549.0 dbar) in the bottle data file. For station 62088 there was no entry for bottle 1 in the bottle file.

References

World Ocean Circulation Experiment (WOCE)

The World Ocean Circulation Experiment (WOCE) was a major international experiment which made measurements and undertook modelling studies of the deep oceans in order to provide a much improved understanding of the role of ocean circulation in changing and ameliorating the Earth's climate.

WOCE had two major goals:

Goal 1. To develop models to predict climate and to collect the data necessary to test them.

Goal 2. To determine the representativeness of the Goal 1 observations and to deduce cost effective means of determining long-term changes in ocean circulation.

UK WOCE

The UK made a substantial contribution to the international World Ocean Circulation Experiment (WOCE) project by focusing on two important regions:

VIVALDI, a seven year programme of seasonally repeated surveys to study the upper ocean.

Long-term observations of ocean climate in the North West Approaches.

Satellite ocean surface topography, temperature and wind data were merged with in situ observations and models to create a complete description of ocean circulation, eddy motion and the way the ocean is driven by the atmosphere.

The surveys were forerunners to the international Global Ocean Observing System (GOOS). GOOS was later established to monitor annual to decadal changes in ocean circulation and heat storage which are vital in the prediction of climate change.

Fixed Station Information

Station Name

WOCE Atlantic Area 12 (AR12)

Category

Offshore area

Latitude

52° 0.00' N

Longitude

18° 0.00' W

Water depth below MSL

World Ocean Circulation Experiment (WOCE) Atlantic Area 12 (AR12)

WOCE was a major international experiment which made measurements and undertook modelling studies of the deep oceans in order to provide a much improved understanding of the role of ocean circulation in changing and ameliorating the Earth's climate. WOCE established numerous areas and repeat sections in the Atlantic Ocean as illustrated in the map below.

AR12 spans the boundary between the subtropical and subpolar gyres in the eastern basin; stations lie within a box bounded by 40.0°N, 35.0°W at the southwest corner and 65.0°N, 03.0°W at the northeast corner The area was occupied between April 1991 to September 1998. A table of all AR12 cruises is presented below: